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doi:10.2204/iodp.pr.308.2005
Expedition 308 began with first line ashore at 1555 h on 30 May 2005.
The IODP technical and Transocean crew changes occurred on schedule on 31 May and 1 June, respectively. In addition to the normal port call routine of loading and unloading freight, offloading cores, a U.S. Coast Guard inspection, Transocean company compliance audit, vessel tours, and the bunkering of fuel (~1300 MT), there were a few nonstandard items related to the special needs of Expedition 308. In anticipation of extremely heavy mud usage during the upcoming expedition, >1000 short tons of bulk material was loaded during the first four days of the port call. Additionally, two service personnel joined the vessel to address specific high-profile aspects of the Gulf of Mexico enterprise; MWD Specialist Hwa Fong "Kelvin" Hoong from Schlumberger and Mud Engineer George Stokes from Milchem International.
The last line was released from the dock at 1455 h on 4 June, and the vessel departed for the first site of Expedition 308 (Table T2).
The JOIDES Resolution arrived at Site U1319 on 6 June and a beacon was deployed at 1350 h. The T2P was first deployed above the seafloor, close to the mudline, to test that it could be deployed through the BHA and that the pressures measured were reasonable. The test was a success. A vibration-isolated television (VIT) survey was conducted prior to spudding. Electrical control problems associated with the mud pumps delayed operations for 45 min, and Hole U1319A was spudded at 0130 h on 7 June. The seafloor depth was estimated to be at 1440.0 meters below rig floor (mbrf) based on core recovery. Piston coring with nonmagnetic hardware advanced to a depth of 114.6 mbsf (Core 13H). Coring was then continued with the extended core barrel (XCB) system to a total depth of 157.5 mbsf. The total average recovery for this hole was 98.6%. The T2P was deployed in Hole U1319A for the first time at a depth of 80.5 mbsf for 30 min, but the tip of the probe was bent because of formation stiffness. The bit was pulled clear of the hole at 2120 h on 7 June and raised to 240 m above the seafloor. The vessel was then offset 2.3 nmi in dynamic positioning (DP) mode to Site U1320 at an average speed of 0.9 kt.
A beacon was dropped at Site U1320A at 0040 h on 8 June. The VIT was launched and the drill string lowered to 1469.6 mbrf. The vessel was offset 5 m north after spotting a man-made object on the seafloor (probably a garbage bag). Hole U1320A was spudded at 0420 h on 8 June. The seafloor depth was established at 1480.4 mbrf based on recovery. Piston coring advanced to 69.4 mbsf where a sandy layer prevented further penetration. Coring continued with the XCB system to 299.6 mbsf (Core 33X). The T2P was deployed at 126.3 (Core 15X) and 231 mbsf (Core 24X), and temperature and pressure were successfully recorded. The first DVTPP temperature measurement was made at 203.4 mbsf (Core 23X) followed by a second measurement at 299.6 mbsf. APC recovery was 101.9%, whereas XCB recovery averaged 78.3%. Recovery for the total cored interval was 83.7%. A supply boat (Emily G) arrived at 0415 h on 10 June to discharge the MWD drilling hardware and departed at 0520 h. Downhole logging of Hole U1320A was undertaken with three tool strings: the triple combo, FMS-sonic, and Well Seismic Tool (WST). All tools reached the bottom of the hole, and good logs were obtained. The VIT was deployed and the hole was observed as the drill string was pulled clear of the seafloor at 1930 h on 10 June. The logging mud quickly obstructed the view, and the camera was promptly recovered.
Hole U1320B was spudded with a MWD drilling assembly at 0915 h on 11 June. The seafloor was established at a depth of 1485.0 mbrf. After washing in the bit to 14.9 mbsf, the VIT was retrieved. MWD drilling was initiated and continued at an average rate of penetration of 25.4 m/h to 320.0 mbsf, which was reached at 0325 h on 12 June. The bit was pulled out of the hole and cleared the seafloor at 0520 h on 12 June. The drill string was positioned 250 m above the seafloor and the vessel was offset 2.3 nmi back to Site U1319 at an average speed of 0.9 kt in DP mode.
The position of Hole U1319B was 20 m north of Hole U1319A. Hole U1319B was spudded at 1105 h on 12 June as the driller observed the bit contacting the seafloor at a depth of 1447.0 mbrf. MWD drilling advanced to 180 mbsf at an average ROP of 30 m/h by 2100 h on 12 June.
The JOIDES Resolution arrived at the location of Site U1321 by 0000 h and a beacon was deployed at 0005 h on 13 June. The driller tagged the seafloor at 1468.0 mbrf (precision depth recorder [PDR] = 1467.4 mbrf) and observed the spudding via the subsea camera at 0205 h. MWD drilling proceeded without incident to the depth objective of 140.0 mbsf by 0900 h at a controlled ROP of 30.0 m/h. The bit was recovered, and the MWD drilling package was disassembled, laid down, and secured for the sea voyage to the next site. The vessel departed for Site U1322 at 1500 h on 14 June.
The 293 nmi transit from Site U1321 to Site U1322 was made at an average speed of 11.0 kt. A beacon was deployed at Site U1321 at 1815 h on 14 June.
Hole U1322A was spudded at 0130 h on 15 June when the driller tagged the seafloor at 1330.0 mbrf (PDR = 1336.4 mbrf). The bit was jetted to 3.8 mbsf, and the VIT was recovered. The hole was then drilled from 3.8 to 200.0 mbsf at an average ROP of 30 m/h. To ensure that we did not exceed our target depth, the interval from 200 to 238.0 mbsf was drilled at an ROP of 20 m/h. There was no indication of pressurized sands throughout the drilled interval. Resistivity and gamma ray data indicated that the main lithology was mud. After the hole was displaced with 70 bbl of 8.9 ppg sepiolite mud, the drill string was pulled out of the hole, clearing the seafloor at 1525 h on 15 June. When the bit was placed at 1040 mbrf (~222 m above seafloor), the DP operator began to offset the vessel to Site U1323. The vessel departed Site U1322 at 1600 h, leaving behind the beacon because of the planned return to this site subsequent to coring operations at Site U1324.
A beacon was deployed at Site U1323 at 1854 h on 15 June. Hole U1323A was spudded at 2025 h as the driller tagged the seafloor at 1271.0 mbrf (PDR = 1278.4 mbrf). The VIT was recovered, and MWD drilling advanced to 206 mbsf. A sand layer, ~1.5 m thick (as interpreted from natural gamma ray resistance data from the MWD bit), was detected at 204 mbsf. Simultaneously, a jump in pressure of 150 psi over the background drilling pressure in the pressure-while-drilling (PWD) log was observed. A residual backpressure of 150 psi was also observed by the driller when he shut down the mud pumps. We pumped 50 bbl of 10.5 ppg mud into the hole and noted that the backpressure went to zero. When this mud was displaced with seawater, the pressure returned. The pipe was filled with 110 bbl of 10.5 ppg mud, and a wiper trip was made to 51.1 mbsf and back to 204.6 mbsf. The overpressure remained, and it was decided to continue to drill ahead at a very low ROP gradually increasing to 30 m/h and with "pumping and dumping" 10.5 ppg mud. At 242 mbsf, a rapid drop in gamma ray resistivity, suggestive of a second sand interval, was observed in the data. At this point, it was decided that to maximize the amount of science and to conserve mud, we should move to the location of Site U1324 and plug and abandon Hole U1323A. We displaced the hole with 73 bbl of 13.5 ppg mud. The VIT was deployed, and the top of the hole was observed to confirm that there was no flow. A free-fall funnel (FFF) was deployed and inspected again with the VIT. We reentered Hole U1323A at 0300 h on 17 June, and the hole was displaced with 31.8 bbl of 14.0 ppg cement that applied a cement plug from 140 to 40 mbsf. The drill string was then recovered, clearing the seafloor at 0550 h and the rotary table at 1010 h on 17 June.
This was the JOIDES Resolution's first experience with riserless drilling with a weighted mud. It was a valuable learning exercise and everyone came away with confidence in the ability to handle downhole pressures in a routine fashion. Provided with accurate real-time downhole information, we confirmed that we can carefully monitor shallow flows, take appropriate action to control the flow, and drill ahead under appropriate conditions. We also demonstrated that we can plug and abandon the hole in this environment without leaving any fluid flow.
A beacon was deployed at Site U1324 at 1040 h on 17 June. Hole U1324A was spudded at 1610 h on 17 June when the driller tagged the seafloor at 1066.0 mbrf (PDR = 1078.0 mbrf). After the bit was washed ahead to 5.0 mbsf, MWD drilling advanced without incident to 333.4 mbsf at an ROP of 30 m/h, where a wiper trip was made back to 60.8 mbsf. MWD drilling resumed to 477.7 mbsf, where another wiper trip was made back to 330.4 mbsf. Because of the potential for interbedded levee sands below 481 mbsf, heavy mud was continuously pumped from this depth to the total depth of 612 mbsf (20 m above the top of the Blue Unit). At ~2045 h on 18 June, MWD drilling advanced slowly at an ROP of 20 m/h and gradually increased to 30 m/h while "pumping and dumping" 10.0 ppg mud. The drilling advanced to the depth objective of 612 mbsf by 0410 h the next morning. The hole was plugged with cement and heavy mud and abandoned. A FFF was made up and deployed at 0808 h on 19 June with the bit at ~80 mbsf. The VIT was deployed, and a visual inspection confirmed that there was no flow emanating from the top of the FFF and that the funnel was upright. The bit was pulled free of the seafloor at 0853 h.
Reentry in Hole U1324A was made at 1828 hr on 19 June and the bit placed at the logging depth of 54.2 mbsf. A tool string consisting of the Hostile Environment Gamma Ray Sonde, DSI, and General Purpose Inclinometer Tool was deployed first. The end of pipe was set at 54.2 mbsf and was later moved to 49 mbsf to ease passage of the logging string. A downhole log was recorded from seafloor at 550 m/s, and we encountered two obstructions at 59 and 509.6 mbsf. The shallow obstruction was passed after a few attempts, but the deeper obstruction remained impassable. After attempting to clear the obstruction for ~15 min and getting some overpull, we decided to log uphole from this point. We measured gamma radiation and P- and S-wave velocity at 15 Hz sampling rate in the first pass at 275 m/h up to 84.0 mbsf. The tool string was lowered for a second pass to 509.6 mbsf, where the same obstruction was encountered. We began the second pass from this depth recording gamma radiation, P- and S-wave velocity, low-frequency lower dipole, and Stoneley modes at 15 Hz sampling rate. The second deployment consisted of the WST. The marine mammal watch began 1 h prior to the WST deployment, and the operation started with putting the generator-injector (GI) gun in the water for the beginning of the soft shooting. The LFV obstructed lowering the WST into the open hole, and we had to pump seawater to ease the tool into the borehole. After this, a bad electrical line prevented power transfer to the main trigger box of the shooting setup. The line was changed, and the computer had to be powered down before the configuration worked. During this time, a corroded plug connecting the electrical leads to the GI gun was also found. This problem was also corrected but delayed the beginning of the experiment by ~1.5 h. Based on LWD caliper recordings, 16 stations were targeted at ~25 m intervals. The Schlumberger equipment was rigged down by 1330 h on 20 June. The hole was then displaced with 44.0 bbl of 11.0 ppg neat cement, forming a 145 m plug. The hole was successfully abandoned at 1745 h when the bit cleared the FFF.
The BHA for Hole U1324B was identical to the BHA used to core the Brazos-Trinity Basin #4 sites. After the VIT performed a survey of the seafloor, the driller tagged the bottom at 1066.8 mbrf. Hole U1324B was spudded with the APC at 0250 h. The recovery of the first core established the seafloor depth at 1067.5 mbrf. Piston coring advanced without incident to a depth of 117.8 mbsf, where the corer did not achieve a complete stroke but did recover 9.91 m (104%). Coring continued with the APC to 357.9 mbsf by advancing by recovery. At this depth, one XCB core was obtained prior to each deployment of the DVTPP and T2P. Piston coring continued to a total depth of 394.5 mbsf by advancing by recovery. A total of 48 piston cores were used in penetrating to this depth (average recovery = 101.3%). Nonmagnetic core barrels were used for all piston cores. The cores were oriented starting with Core 4H. The APCT was deployed in 14 cores, and a special Fugro cutting shoe was deployed in Cores 4H, 7H, and odd-numbered piston cores up to and including 49H. Coring resumed with the XCB and deepened the hole to 608.2 mbsf. The XCB-cored portion of the hole was 223.8 m with an average recovery of 80.8%. The total cored interval of 608.2 m was obtained with 93.7% average recovery. In compliance with the operational protocol, heavy mud (10.5 ppg) was continuously pumped starting at 481 mbsf and sustained until the bottom of the hole. The DVTPP was deployed 10 times in this hole (229.1, 362.4, 387.9, 464.3, 493.1, 522.0, 541.2, 560.4, 589.2, and 608.3 mbsf). There were also 10 deployments (~30 min each) of the T2P (51.3, 89.3, 117.8, 136.3, 368.0, 394.5, and 593.2 mbsf). In accordance with the operating protocol, the hole was plugged with 44 bbl of 11.0 ppg neat cement forming a plug of ~145 m. The cement was followed by 40 bbl of 10.5 ppg mud and then chased with 50 bbl of seawater. The hole was observed by the VIT camera with the bit at ~80 mbsf, and no flow was detected. The bit was pulled free of the hole at 0025 h on 26 June. As the vessel was moved off location, a subsea release dart was pumped down to swab the inside of the pipe.
The vessel was dynamically repositioned 20 m west of Hole U1324A. After a VIT survey of the seafloor of the new hole failed to indicate any obstructions, Hole U1324C was spudded when the driller tagged the seafloor at 1066.5 mbrf. The hole was then drilled ahead to 50.0 mbsf, where the T2P was deployed with good results. Following the retrieval of the probe, a single APC core was obtained for physical property analysis. The hole was then drilled in increments of 50 m, alternating between T2P and DVTPP deployments and taking APC cores for geotechnical analysis. Operations in Hole U1324C continued with the deepening of the hole to 250.0 mbsf, where a DVTPP measurement was taken followed by a single piston core. The hole was then drilled from 250.0 to 300.0 mbsf, where the fifth T2P deployment was made, followed by a single piston core. The hole was then drilled to 405.0 and 505.0 mbsf, followed each time by a single piston core. The last piston cored advanced to a final depth of 511.8 mbsf. When the driller advanced beyond 481.0 mbsf, heavy mud (10.5 ppg) was continuously pumped in accordance with the operating protocol for this site. A total of eight piston cores were obtained, with the last seven advanced by recovery. The cored interval was 55.1 m with an average recovery of 100.9%. Before the drill string was withdrawn from Hole U1324C, the hole was observed by VIT camera and no flow was evident. Because penetration in the hole was terminated above the sand layers, it was not necessary to plug this hole with cement. The bit was pulled free of the seafloor at 0135 h on 28 June and positioned 204 m above the seafloor. The beacon was recovered before departing location at 0240 h.
The vessel was offset 6.2 nmi to Site U1322 at 0915 h on 28 June. After observing the seafloor with the VIT camera, Hole U1322B was spudded with the APC at 1145 h. Piston coring advanced the hole to a depth of 61.0 mbsf when operations were interrupted because of the failure of a control transformer in the variable field supply of the core winch. This required 3.75 h to troubleshoot and repair. Piston coring resumed at 2345 h on 28 June and continued to 0730 h on 30 June, when the total depth of 234.5 mbsf was attained. The average recovery for the hole was 101.0%. The T2P was deployed three times in this hole. The first measurement in the hole was made at 42.0 mbsf following Core 5H. The second attempt was made at 134.3 mbsf subsequent to Core 15H. On this occasion, the hole was displaced with 10.5 ppg mud. The last deployment was at a depth of 157.8 mbsf. This deployment was made after recovering Core 18H and with the hole displaced with 55 bbl of 10.5 ppg mud. The DVTPP was deployed once at a depth of 166.7 mbsf following Core 19H. On this occasion, the hole was displaced with 55 bbl of 10.5 ppg mud. The bit was pulled free of the hole at 1010 h on 30 June.
Hole U1322C was dedicated to temperature and pressure measurements. Following a DP offset of 20 m west of Hole U1322A, the VIT was deployed. The visual examination of the seafloor confirmed a clear area under the bit. Hole U1322C was spudded with the APC at 1125 h on 30 June. Hole U1322C was then drilled in six intervals to a final depth of 231.5 mbsf. The T2P was deployed at 50, 75, 150, and 200 mbsf. After the first measurement attempt, the hole was stabilized by displacing it with 10.5 ppg mud. The DVTPP was deployed at 100, 220, and 238 mbsf. The hole was also displaced with heavy mud prior to each deployment, and no circulation or rotation was applied. The hole was displaced with an additional 75 bbl of 10.5 ppg mud prior to abandonment. The bit cleared the seafloor at 1824 h on 1 July and was observed with the VIT. No flow was emanating from this hole. While operating in Hole U1322C, the Emily G made the third and final visit to the JOIDES Resolution. The Emily G was on location and standing by at 0400 h on 30 June. The work boat offloaded catering supplies and loaded freight originally destined for Panama. We also loaded 35.5 short tons (710 sacks) of Florigel (attupulgite) from the Emily G. The work boat departed for Port Fourchon, Louisiana at 0930 h transporting Mud Engineer George Stokes and two other personnel (IODP Marine Laboratory Specialist Karen Johnston and Transocean DP Operator John Powell) to shore.
The vessel was offset 20 m north of Hole U1322A, where Hole U1322D was spudded with the APC at 1925 h on 1 July. This followed a seafloor survey with the VIT. The hole was drilled and cored in five incremental steps to a total depth of 175.0 mbsf. Three piston cores were obtained from the seafloor to 9.5 mbsf, 70.0–79.5 mbsf, and 100.0–107.8 mbsf. The average recovery of the cored interval of 26.8 m was 101.5%. The T2P was deployed four times at 40.0, 70.0, 100, and 134 mbsf. The DVTPP was deployed at 175.0 mbsf. With the exception of the first T2P run, the holes were displaced with heavy mud prior to deployment, and all downhole measurements were attempted with no circulation or rotation. All operations concluded by 1600 h on 2 July to allow sufficient time to recover the drill string, beacons, and disassemble and store the BHA components. The VIT was deployed prior to withdrawal of the drill string from the hole, and a short inspection of the top of Hole U1322D confirmed the absence of any flow.
After the drilling equipment was secured, the vessel began the voyage to Panama at 0030 h on 3 July.
Expedition 308 officially ended with the first line ashore at 1420 h on 8 July 2005.